µ-Pyrazolato-µ-carboxylato- and di(µ-pyrazolato)dimanganese(II) complexes: synthesis, characterization and catalase-like function

Abstract

3,5-Bis[N,N-di(2-pyridylmethyl)aminomethyl]pyrazole (HL¹) and 3,5-bis[N,N-bis(2-diethylaminoethyl)aminomethyl]pyrazole (HL²) formed µ-pyrazolato-µ-carboxylato-dimanganese(II) complexes [Mn₂L(O₂CR)][BPh₄]₂(L = L¹, R = Ph; 1; L = L², R = Me 2) and 3,5-bis[N-(2-pyridylmethyl)aminomethyl]pyrazole (HL³) gave a di(µ-pyrazolato)-dimanganese(II) complex [Mn₂L³₂][BPh₄]₂3. The ditoluene adduct of 3 crystallizes in the triclinic space group P with a= 14.452(3), b= 15.573(5), c= 10.988(4)Å, α= 108.78(3), β= 93.31(2) and γ= 115.10(2)°. X-Ray diffraction analysis revealed a di(µ-pyrazolato)-dimanganese(II) core with Mn ⋯ Mn separation 4.181(2)Å. All the complexes showed catalytic activity towards disproportionation of H₂O₂ in dimethylformamide at 0 °C. The initial rate of dioxygen evolution in the presence of 1 is first order in both the complex concentration and that of H₂O₂; v=k[Mn₂][H₂O₂], k= 1.45 dm³ mol^–1 s^–1. Together with the observation of a ligand-to-metal charge-transfer band characteristic of Mn^IVO in the catalysis by 2, a mechanistic scheme involving a cycle from {Mn^III(OH)}₂ to {Mn^IV(O)}₂ is inferred. In the disproportionation by 3 the initial rate of evolution is first order in complex concentration and second order in that of H₂O₂; v=k[Mn₂][H₂O₂]², k= 29 dm⁶ mol^–2 s^–1).